Composite Materials Research Progress

Multi-scale Analysis of Fiber-Reinforced Composite Parts… 3
of the constituents, the lay-up configuration, ... fall in this last category of factors). Now, the
knowledge of internal stresses is necessary to predict a possible damage occurrence in the
material during its manufacturing process or service life. Thus, the study of the development
of internal stresses due to thermo-hygro-elastic loads in composites is very important in
regard to any engineering application. Numerous papers, available in the literature, deal with
this question, using Finite Element Analysis or Continuum Mechanics-based formalisms.
These methods allow the calculation of the macroscopic stresses in each ply constituting the
composite (Jacquemin and Vautrin, 2002). But, they do not provide information on the local
mechanical states, in the fibers and matrix of a given ply, and, consequently, do not allow to
explain the phenomenon of matrix cracking and damage development in composite structures,
which originate at the microscopic level. The present work is precisely focused on the study
of the internal stresses in the constituents of the ply. In order to reach this goal, scale
transition models are required.
The present work underlines the potential of scale-transition models, as predictive tools,
complementary to continuum mechanics in order to address: i) the estimation of the effective
hygro-thermo-elastic properties of a composite ply from those of its constituents (section 2),
ii) the identification of the hygro-thermo-elastic properties of one constituent of a composite
ply (section 3), iii) the estimation of the local mechanical states experienced in each
constituent of a composite structure (section 4), iv) the identification of the local strength of
the constitutive matrix (section 5).
Section 6 of this paper is mainly dedicated to conclusions about the above listed sections
the whereas section 7 is devoted to the introducing some scientifically appealing perspectives
of research in the field of composites materials which are highly considered for further
investigation in the forthcoming years.
2. Scale-Transition Model for Predicting the Macroscopic
Thermo-Hygro-Elastic Properties of a Composite Ply
2.1. Introduction
Scale transition models are based on a multi-scale representation of materials. In the case of
composite materials, for instance, a two-scale model is sufficient:
- The properties and mechanical states of either the resin or its reinforcements are
respectively indicated by the superscripts m and r . These constituents define the socalled
“pseudo-macroscopic” scale of the material (Sprauel and Castex, 1991).
- Homogenisation operations performed over its aforementioned constituents are
assumed to provide the effective behaviour of the composite ply, which defines the
macroscopic scale of the model. It is denoted by the superscript I . This definition
also enables to consider an uni-directional reinforcement at macroscopic scale, which
is a satisfactorily realistic statement, compared to the present design of composite
structures (except for the particular case of woven-composites that will be
specifically discussed in section 7.1).